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Bob Cozzi wrote:
Actually Hans, that's not it at all.
If I have a display file with one or two date fields in it (and we're
talking RPGIII here) I would rather write two MULT and get it done than
worry about setting up a DS in RPGIII and moving the bytes around.
If I were reading say 100,000,000 database records and converting a date
field in them, then I would probably use the DS method.
-Bob
Bob: You might find this hard to believe, but I think I've changed my
mind on this issue.
First, consider performance. Sure, doing a couple of subfield moves is
faster than using the MULT trick. But the MULT trick is still ~35 times
faster than doing things the proper way, converting to and from a date
value!
Second, and perhaps more importantly, consider code readability. Sure,
seeing a MULT by 100000.0001 (or whatever) is cryptic. But so is a
sequence of moves. Sure, not everyone knows the "trick". But when it's
explained, it just becomes another idiom in the language. Much of what a
programmer does involves learning and mastering language idioms.
That's not to say I will recommend the use of the MULT date conversion
trick. But I agree with you - I really don't see any reason not to use
it either when appropriate if you can't do the "right" thing and use the
date datatype.
BTW, out of curiosity, I did a bit of performance comparison as I was
putting this note together. Here are the times for equal iterations of
alternative statements:
# time statement
- ---- --------------------------------------------------
1: 6982: dmdy = %dec(%date(dymd:*iso):*usa);
2: 1038: dmdy = %int(%subst(%char(dymd)+%char(dymd):5:8));
3: 190: C dymd mult 10000.0001 dmdy
4: 64: ds.num = dymd;
ds = %subst(ds:5:4) + %subst(ds:1:4);
dmdy = ds.num;
Statement #1 is the date conversion done "properly" using conversion to
and from date type. Statement #2 sort of does the MULT trick but using
character manipulation in a free-form calc. Statement #3 is the MULT
trick. #4 converts the date using manipulation of DS subfields.
Clearly, using date data type is the slowest. But also, it would appear
that the MULT trick isn't nearly as bad relative to subfield moves as it
used to be.
Cheers! Hans
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